Synthetic leather has been used in a wide variety of fields such as interior materials for automobiles and railways, and interior materials for buildings and furniture as a substitute for natural leather. Synthetic leather used as an interior material for vehicles such as automobiles or a cover material for furniture is desired to have soft feeling, flexibility, mechanical strength and durability. Since it is easily burnt, it needs to be flame retardant. For example, there are FMVSS-302 and JIS-D-1201 for interior materials for automobiles, a 45° ethyl alcohol method, which is a non-metal material testing method for rail cars, for interior materials for railways, and JIS-A-1321 for wall covering materials. High flame retardancy which meets these standards is required.
Synthetic leather is formed by laminating a surface resin layer of polyurethane, polyolefin or polyvinyl chloride on a fiber substrate such as a woven, knitted or nonwoven fabric. An adhesive layer may be existent between the fiber substrate and the surface resin layer.
As for the flame retardation of synthetic leather, a method for flame retarding at least one of the fiber substrate, the surface resin layer and the adhesive layer is reported, and a halogen-based compound or a combination of a halogen-based compound and antimony oxide is effective as a flame retardant in use. However, in recent years, flame retardation without using a halogen-based flame retardant has been desired from the viewpoint of environmental conservation and a harmful effect of a gas generated at the time of combustion. As the non-halogen-based flame retardant, there are known a large number of flame retardants such as ammonium phosphate, ammonium sulfamate, ammonium sulfate, borax, boric acid, ammonium hydroxide, magnesium hydroxide and phosphoric acid esters (Patent Documents 1 to 4).
However, when a water-soluble flame retardant is added in an amount required for the production of a flame retarding effect, there occur problems such as the thickening of a synthetic resin emulsion or solution, destruction (gum-up), the deterioration of the strength of a resin film, heat resistance and feeling. Since ammonium polyphosphate which contains no halogen and has a flame retarding effect relatively has water solubility, it elutes into water and causes problems with the physical properties and flame retardancy of a product under the condition that water resistance is required. Further, even ammonium polyphosphate which is capsulated with an improved resin is not satisfactory in terms of water resistance. Therefore, synthetic leather which has satisfactory flame retardancy and physical properties by using a phosphorus-based flame retardant and not a halogen-based flame retardant is not provided yet.
(Patent Document 1) JP-A 01-260072
(Patent Document 2) JP-A 2005-015942
(Patent Document 3) JP-A 2009-019304
(Patent Document 4) JP-A 2009-209489